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The Agb Newsletter THE AGB NEWSLETTER An electronic publication dedicated to Asymptotic Giant Branch stars and related phenomena Official publication of the IAU Working Group on Abundances in Red Giants No. 160 — 2 November 2010 http://www.astro.keele.ac.uk/AGBnews Editors: Jacco van Loon and Albert Zijlstra Editorial Dear Colleagues, It is our pleasure to present you the 160th issue of the AGB Newsletter. Enjoy it! Notwithstanding the economic recession, there still are jobs for astronomers! There is a Ph.D. studentship offered to work with Isabelle Cherchneff in Switzerland, and there are three post-doctoral fellowships offered to work on the planned HERMES spectrograph surveys in Australia. ALMA is growing fast and the call for early-science observations is imminent. Various workshops are being organised to prepare the community for this, one of which takes place in Manchester in December. There is a special AGB (and ”related” objects) meeting associated with it as well. The next issue is planned to be distributed on the 1st of December 2010. Editorially Yours, Jacco van Loon and Albert Zijlstra Food for Thought This month’s thought-provoking statement is: What should we make sure ALMA does to advance our understanding of AGB stars? Reactions to this statement or suggestions for next month’s statement can be e-mailed to [email protected] (please state whether you wish to remain anonymous) 1 Refereed Journal Papers The UK infrared Telescope M 33 monitoring project. I. Variable red giant stars in the central square kiloparsec Atefeh Javadi1,2, Jacco Th. van Loon2 and Mohammad Taghi Mirtorabi1 1Physics Department, Alzahra University, Vanak, Tehran, Iran 2Astrophysics Group, Lennard-Jones Laboratories, Keele University, Staffordshire ST5 5BG, UK We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope (UKIRT), of the Local Group spiral galaxy M 33 (Triangulum). The main aim was to identify stars in the very final stages of their evolution, and for which the luminosity is more directly related to the birth mass than the more numerous less-evolved giant stars that continue to increase in luminosity. The most extensive dataset was obtained in the K-band with the UIST instrument for the central 4′ × 4′ (1 kpc2) – this contains the nuclear star cluster and inner disc. These data, taken during the period 2003–2007, were complemented by J- and H-band images. Photometry was obtained for 18,398 stars in this region; of these, 812 stars were found to be variable, most of which are Asymptotic Giant Branch (AGB) stars. Our data were matched to optical catalogues of variable stars and carbon stars, and to mid-infrared photometry from the Spitzer Space Telescope. In this first of a series of papers, we present the methodology of the variability survey and the photometric catalogue – which is made publicly available at the Centre de Donn´eesastronomiques de Strasbourg (CDS) – and discuss the properties of the variable stars. Most dusty AGB stars had not been previously identified in optical variability surveys, and our survey is also more complete for these types of stars than the Spitzer survey. Accepted for publication in MNRAS Available from arXiv:1009.1822 The SAGE-Spec Spitzer Legacy program: The life-cycle of dust and gas in the Large Magellanic Cloud. Point source classification I. Paul M. Woods1, J.M. Oliveira2, F. Kemper1, J.Th. van Loon2, B.A. Sargent3, M. Matsuura4,5, R. Szczerba6, K. Volk3, A.A. Zijlstra1, G.C. Sloan7, E. Lagadec8,1, I. McDonald1, O. Jones1, V. Gorjian9, K.E. Kraemer10, C. Gielen11, M. Meixner3, R.D. Blum12, M. Sewi lo3, D. Riebel13, B. Shiao3, C.-H.R. Chen14, M.L. Boyer3, R. Indebetouw14,15 and the SAGE-Spec team 1Jodrell Bank Centre for Astrophysics, Manchester, UK 2Keele University, UK 3Space Telescope Science Institute, USA 4University College London, UK 5Mullard Space Science Laboratory, UK 6N. Copernicus Astronomical Center, Poland 7Cornell University, USA 8ESO, Germany 9JPL/Caltech, USA 10US Air Force Research Laboratory, USA 11Katholieke Universiteit Leuven, Belgium 12NOAO, USA 13Johns Hopkins University, USA 14University of Virginia, USA 15NRAO, USA We present the classification of 197 point sources observed with the Infrared Spectrograph in the SAGE-Spec Legacy program on the Spitzer Space Telescope. We introduce a decision-tree method of object classification based on infrared 2 spectral features, continuum and spectral energy distribution shape, bolometric luminosity, cluster membership, and variability information, which is used to classify the SAGE-Spec sample of point sources. The decision tree has a broad application to mid-infrared spectroscopic surveys, where supporting photometry and variability information are available. We use these classifications to make deductions about the stellar populations of the Large Magellanic Cloud and the success of photometric classification methods. We find 90 asymptotic giant branch (AGB) stars, 29 young stellar objects, 23 post-AGB objects, 19 red supergiants, eight stellar photospheres, seven background galaxies, seven planetary nebulae, two H ii regions and 12 other objects, seven of which remain unclassified. Accepted for publication in Monthly Notices of the RAS Available from arXiv:1009.5929 Hot Bottom Burning in the envelope of SAGB stars Paolo Ventura1 and Francesca D’Antona1 1Observatory of Rome, Italy We investigate the physical and chemical evolution of population II stars with initial masses in the range 6.5–8 M⊙, which undergo an off centre carbon ignition under partially degenerate conditions, followed by a series of thermal pulses, and supported energetically by a CNO burning shell, above a O–Ne degenerate core. In agreement with the results by other research groups, we find that the O–Ne core is formed via the formation of a convective flame that proceeds to the centre of the star. The evolution which follows is strongly determined by the description of the mass loss mechanism. Use of the traditional formalism with the super-wind phase favours a long evolution with many thermal pulses, and the achievement of an advanced nucleosynthesis, due the large temperatures reached by the bottom of the external mantle. Use of a mass loss recipe with a strong dependence on the luminosity favours an early consumption of the stellar envelope, so that the extent of the nucleosynthesis, and thus the chemical composition of the ejecta, is less extreme. The implications for the multiple populations in globular clusters are discussed. If the “extreme” populations present in the most massive clusters are a result of direct formation from the super-AGB ejecta, their abundances may constitute a powerful way of calibrating the mass loss rate of this phase. This calibration will also provide informations on the fraction of super-AGBs exploding as single e-capture supernova, leaving a neutron star remnant in the cluster. Accepted for publication in MNRAS Available from arXiv:1009.4527 Seismic diagnostics of red giants: First comparison with stellar models Josefina Montalb´an1, Andrea Miglio1, Arlette Noels1, Richard Scuflaire1 and Paolo Ventura2 1Institut d’Astrophysique et G´eophysique, Universt´ede Li`ege, Belgium 2Osservatorio Astronomico di Roma–INAF, Italy The clear detection with CoRoT and KEPLER of radial and non-radial solar-like oscillations in many red giants paves the way for seismic inferences on the structure of such stars. We present an overview of the properties of the adiabatic frequencies and frequency separations of radial and non-radial oscillation modes for an extended grid of models.We highlight how their detection allows a deeper insight into the internal structure and evolutionary state of red giants. In particular, we find that the properties of dipole modes constitute a promising seismic diagnostic tool of the evolutionary state of red giant stars.We compare our theoretical predictions with the first 34 days of KEPLER data and predict the frequency diagram expected for red giants in the CoRoT exofield in the galactic center direction. Published in Astrophysical Journal Letters Available from arXiv:1009.1754 and from http://iopscience.iop.org/2041-8205/721/2/L182/ 3 The ubiquity of the rapid neutron-capture process Ian U. Roederer1, John J. Cowan2, Amanda I. Karakas3,4, Karl-Ludwig Kratz5, Maria Lugaro4, Jennifer Simmerer6, Khalil Farouqi7 and Chris Sneden8 1Carnegie Observatories, USA 2Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, USA 3Research School of Astronomy & Astrophysics, The Australian National University, Mount Stromlo Observatory, Australia 4Centre for Stellar and Planetary Astrophysics, School of Mathematical Sciences, Monash University, Australia 5Max-Planck-Institut f¨ur Chemie, Otto-Hahn-Institut, Germany 6Department of Physics and Astronomy, University of Utah, USA 7Zentrum f¨ur Astronomie der Universit¨at Heidelberg, Germany 8Department of Astronomy, University of Texas at Austin, USA To better characterize the abundance patterns produced by the r-process, we have derived new abundances or upper limits for the heavy elements zinc (Zn, Z = 30), yttrium (Y, Z = 39), lanthanum (La, Z = 57), europium (Eu, Z = 63), and lead (Pb, Z = 82). Our sample of 161 metal-poor stars includes new measurements from 88 high resolution and high signal-to-noise spectra obtained with the Tull Spectrograph on the 2.7m Smith Telescope at McDonald Observatory, and other abundances are adopted from the literature. We use models of the s-process in AGB stars to characterize the high Pb/Eu ratios produced in the s-process at low metallicity, and our new observations then allow us to identify a sample of stars with no detectable s-process material. In these stars, we find no significant increase in the Pb/Eu ratios with increasing metallicity. This suggests that s-process material was not widely dispersed until the overall Galactic metallicity grew considerably, perhaps even as high as [Fe/H] = −1.4, in contrast with earlier studies that suggested a much lower mean metallicity.
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